The present invention relates to a plastics processing machine, in particular to an injection molding machine or an extruder, and more particularly to a plastics processing machine having at least one component being controlled by a control device.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
German Offenlegungsschrift DE 199 58 790 C2 discloses a machine for making parts of plastic or rubber, whereby an electronic unit, which is mounted in a plug on the machine, forms part of the control device of the machine and assumes detection of the actual temperature value with linearization and cold-spot compensation. The connection between the electronic unit and the control device is realized via a field bus.
As a consequence of an ever increasing automation, machine tools, like e.g. CNC milling machines or presses, use so-called automated tool recognition systems. Hereby it is to be understood the encoding of replacement tools by means of a chip which either contains the tool number only, whereas the CNC has stored the tool-specific parameters for this tool number, or contains per se the tool-specific parameters. Such a system is described, for example, in the “interbus applications”, release 02/1998 by the INTERBUS Club. Through automated tool recognition the previously used so-called space encoding is improved and rendered flexible which involves the assignment to each tool of precisely one space where it is deposited. To provide each tool with its own chip and to provide the machine with a respective reading station is cost-effective only because of the very frequent change of tools in machine tools.
Plastics processing machines normally include a plurality of partly very complex components, among others a clamping unit, a feed and metering apparatus, a plasticizing unit or extruder. Within these components, oftentimes various configurations of elements are possible whose specific parameters must be taken into account by a control device of the machine when controlling the component. For example, a plasticizing unit or an extruder includes a screw rotating in a screw cylinder for plasticizing and thoroughly mixing the material to be processed. Depending on need, plastics processing machines may be outfitted with different configurations between screw cylinder and used screw which in turn has its own characteristics. Unlike machine tools, a configuration is involved here which oftentimes does not change oftentimes.
The crucial criteria for selection of screw and cylinder are i.a. the intended field of application and the nature of the material to be processed. The greatest transmittable torque, the greatest applicable speed, the greatest applicable injection pressure, and the greatest injection stroke depend for example on the selection of the configuration. This represents however only some of the variables that are determined by the structure of the screw, like e.g. the number and shape of the grooves and the length/diameter ratio, and by the properties of the used cylinder. Typical characteristics of a cylinder are for example the diameter, the surface finish, the number of external heating zones, i.e. the number of separately operable and heatable zones along the length extension of the cylinder, the heating or cooling capacity that can be introduced there, type and characteristics of the thermoelectric elements used as temperature sensors, to name only a few. In conformity with the screw to be used and the cylinder as well as the material to be processed, the possible areas of use of a screw cylinder combination is determined.
As all component-specific parameters must be considered when correctly operating a component by a control device of a plastics processing machine, the control programs running in the control device must be separately suited to each possible component configuration when shipped. This means for example in relation to the plasticizing unit which is used in many different screw-cylinder configurations a very complicated programming process for each delivered machine. This is also a major drawback in connection with possible changes of an existing screw-cylinder configuration, as can be encountered in the exceptional case during material change but in particular upon replacement of defective or worn screws by new ones. The continuous adjustment of the control software is also a source of errors as is any change of existing software.
Compounding this problem is the fact that this special need for customization up to now did not enable the use of a uniform control software which would be applicable for all offered components which are combined for various customers in a machine according to a modular concept, and especially for different screw-cylinder configurations. This is however of great interest in particular for certain diameter zones in relation to the screw, paired with certain second diameter zones in relation to the cylinder.
A further drawback resides in particular in connection with screw-cylinder configurations in the complicated wiring that is required when changing the used external heating zones and especially when exceeding a certain standard number in order to ensure correct temperature compensation by means of a compensating wiring. Such a temperature compensation is required when using thermoelectric elements as temperature sensors to avoid corruption of the voltage supplied by the thermoelectric elements.
It would therefore be desirable and advantageous to provide a possibility to allow application of numerous components in specific configuration, in particular plasticizing and injection units with various screw-cylinder configurations in plastics processing machines while requiring little program adjustments, and allowing use of a global control software which is as configuration-independent as possible.